In many beverage preparing apparatuses, at some stage in the preparation process, the beverage or some fluid ingredient thereof is passed along a heat exchanging section so as to heat or cool said fluid to a desired temperature. For instance, when preparing baby milk from water and formula, the water may first be passed along heating means to sanitize the water and subsequently be passed along cooling means to cool down the water to a suitable consumption temperature. The exact temperature of the fluid that leaves said heat exchanging section may vary, depending on for instance the temperature of the fluid when it enters the section, the flow rate through the section, etc.
To control said temperature more accurately, a valve assembly may be provided for mixing the fluid with a colder or hotter version of itself, which colder or hotter version may be tapped from some upstream or downstream point in the apparatus or some external source. To set the appropriate mixing ratio between said fluids, known mixing valves are provided with a heat sensitive body that expands when the temperature of the mixed fluids deviates from a desired temperature. This expansion causes the inflow of one of the fluids to be reduced and consequently the mixing ratio and resulting mixing temperature to be changed.
A disadvantage of these known mixing valves is that the heat sensitive body needs a rather large flow rate to function properly. Such large flow rate will usually not be available in an apparatuses according to the invention. And when it is available, such large flow rate will cause a large amount of too cold or too hot fluid to have passed the valve by the time that the valve has reached its optimum setting. Also, the output flow of the known mixing valves varies depending on the selected mixing ratio. Consequently, when the mixing valve is to supply a specific amount of fluid (which will often be the case in an apparatus according to the present invention) a special flow rate sensor or other suitable sensor will be needed for metering the desired quantity. This renders the apparatus more costly and complex.
Therefore, there exists a need for an improved temperature control valve assembly for use in apparatuses which operate with relatively small but preferably constant flow rates, such as apparatuses for preparing a beverage.